Apple does not have a monopoly on Smart Phones or App Stores. They're able to as much as anyone to control how their platform is used - there's no law against maintaining a closed and curated platform and your product or platform is not considered a Market in by itself.
There's also no law against having a monopoly, only for abusing your monopoly in one market to gain an unfair advantage in a different one.
There's also no law against having a monopoly, only for abusing your monopoly in one market to gain an unfair advantage in a different one.